Trapping device, processing system, and method removing impurities

ABSTRACT

A trapping device is disclosed which is arranged in a vacuum exhaust system ( 6 ) for removing gaseous impurities contained in the exhaust gas flowing through the vacuum exhaust system ( 6 ) which has a vacuum pump ( 36 ) for vacuum exhausting a processing unit ( 10 ) wherein a certain process is conducted on a semiconductor wafer. The trapping device comprises an impurity collecting chamber ( 50 ) arranged along the exhaust passage in the vacuum exhaust system ( 6 ) and a nozzle means ( 64 ) which injects a working fluid that is in a supersonic state due to adiabatic expansion for mixing the fluid with the exhaust gas and lowering the temperature of the exhaust gas to or below the critical points of the impurities within the impurity collecting chamber ( 50 ).

FIELD OF THE INVENTION

The present invention relates to a trap apparatus, a processing system,and an impurity removal method for removing gaseous impurities from anexhaust gas discharged from a processing apparatus such as a filmforming apparatus or the like.

BACKGROUND OF THE INVENTION

Generally, for forming an integrated circuit such as an IC or a logicdevice, there are repeatedly performed a process for forming a desiredthin film on a surface of a semiconductor wafer, a glass substrate, anLCD substrate or the like; and a process for etching it in a desiredpattern.

For example, in a film forming process, a specified processing gas(source gas) reacts in a processing vessel to form a silicon thin film,a thin film of a silicon oxide or nitride, or a metal thin film, a thinfilm of a metal oxide or metal nitride, or the like. As a result of thefilm forming process, residual reaction by-products are produced to bedischarged with an exhaust gas. In addition, an unreacted processing gasis discharged.

If the reaction by-products or the unreacted processing gas aredischarged into the air as they are, they may cause environmentalpollution and the like. For preventing this, conventionally, a trapapparatus has been installed in an exhaust gas system extending from aprocessing vessel. In this way, the reaction by-products, the unreactedprocessing gas and the like, which are contained in the exhaust gas,have been collected and removed.

Various configurations of the trap apparatus have been proposed based oncharacteristics of the reaction by-products and the like that must becollected and removed. For example, in case of removing reactionby-products, which are condensed (liquefied) and/or coagulated(solidified) at room temperature, the trap apparatus can be configuredsuch that multiple fins are provided in a housing having an inletopening and an outlet opening of the exhaust gas. The fins aresequentially arranged along a flow direction of the exhaust gas, and thereaction by-products in the exhaust gas are collected by surfaces of thefins by being attached thereon when the exhaust gas passes between thefins. Further, the fins have been cooled by a cooling fluid to increasecollection efficiency.

Here, as an example, a case where a Ti metal film is formed by using asa source gas a refractory metal halogen compound, i.e., TiCl₄ (titaniumtetrachloride), will now be explained. H₂ gas as well as TiCl₄ is usedas the source gas, and these gases are activated by a plasma in thepresence of Ar gas to thereby be reduced by hydrogen. As a result, theTi film is deposited on a surface of the semiconductor wafer. During theprocess, TiCl_(x) (X<4) is produced as a reaction by-product and therealso exists an unreacted TiCl₄ gas, which are discharged as the exhaustgas. Since these TiCl_(x) and TiCl₄ are impurity gases causing airpollution and the like, they are trapped by such a trap apparatus.

Here, the impurity gases such as the above-described TiCl₄ as theunreacted gas, TiCl_(x) as the reaction by-product and the like, haverelatively high vapor pressures, so that it is very difficult tocompletely trap and remove them in the trap apparatus, even when thetrap apparatus is cooled as mentioned above. Thus, satisfactory recoveryrate could not be realized. For completely removing the impurity gasespassing through the trap apparatus and making them harmless, there hasbeen provided a waste gas scrubber at a downstream side of the trapapparatus, which gives rise to soaring running cost of the waste gasscrubber and shortening of life span thereof. Such problems are commonto the film forming apparatus, which employs a refractory metal compoundgas such as TiCl₄, WF₆, (Ta(OE)₅)₂ or the like.

As for another film forming method using TiCl₄, there has been known amethod for forming a TiN film. Namely, as an example, a case where a TiNfilm is formed by using as a source gas a refractory metal halogencompound, i.e., TiCl₄ (titanium tetrachloride), will now be explained.NH₃ gas as well as TiCl₄ is used as the source gas, and both gases reactwith each other to deposit the TiN film on a surface of thesemiconductor wafer. At this time, NH₄Cl or TiCl₄(NH₃)_(n) (n is apositive integer) is produced as the reaction by-product, and anunreacted TiCl₄ gas is also present. These gas components are dischargedas the exhaust gas to be trapped by the aforementioned trap apparatus.

Further, in order to more completely remove the impurity gas, e.g., achloride gas, contained in the exhaust gas, there has been proposed amethod for efficiently removing the impurity gas by mixing the exhaustgas in a gas exhaust system with a reactive gas, e.g., an ammonium gas,which reacts with the impurity gas, to convert the impurity gas into,e.g., an ammonium chloride, which is likely to be condensed; and bycooling and condensing the ammonium chloride in the trap apparatus to betrapped therein (Japanese Patent Laid-open Application No. 2001-214272).

Still further, in Japanese Patent Laid-open Application No. S62-4405,there has been disclosed a technology wherein circular trap plateshaving small holes are placed in multi-levels inside a wax trapapparatus such that an exhaust gas passing through the small holes iscooled by a self-cooling while being adiabatically expanded, to therebyliquefy a wax to be collected, when liquefying the wax in the exhaustgas containing a wax vapor discharged from a sintering furnace forsintering a powder molding product and collecting it therefrom.

However, in the conventional trap apparatus as described in theaforementioned Japanese Patent Laid-open Application No. 2001-214242, ifcaptured materials are attached to the cooling fins as the trap processprogresses, cooling efficiency of the exhaust gas gets declined sincethe exhaust gas exchanges heat with the cooling fins through a capturedmaterial layer. For the same reason, collection efficiency becomeslowered due to aging, so that the impurity gases could not be completelyremoved and the increasing in the frequency of maintenance and repairbecomes problematic. For preventing deterioration of collectionefficiency due to aging, it may be considered that the cooling fins areset in multi-levels. However, it is impractical since the apparatusbecomes significantly enlarged in this case. Moreover, in case ofremoving the captured materials from the cooling fins by a cleaningoperation during the maintenance and repair, it becomes difficult toperform the cleaning operation since the cooling fins are formed inmulti-levels, and thus a whole structure is complicated.

Further, in the trap apparatus as described in Japanese Patent Laid-openApplication No. S62-4405, in case where the captured materials are of asemisolid mass having a viscosity, the small holes of the circular trapplate are getting clogged with the captured materials, so that theincreasing in the frequency of maintenance and repair becomesproblematic.

Still further, in the trap apparatus as described in Japanese PatentLaid-open Application No. S62-4405, cooling efficiency is not very highsince the exhaust gas is adiabatically expanded through the small holes.Thus, the impurity gas in the exhaust gas is not fully collected,thereby lowering collection efficiency.

SUMMARY OF THE INVENTION

The present invention is contrived on the basis of the aforementionedproblems and is to solve them effectively. It is, therefore, an objectof the present invention to provide a trap apparatus, a processingsystem and an impurity removal method for removing gaseous impuritiesfrom an exhaust gas, wherein a simple structure is employed andcollection efficiency can be kept high all the time.

As a result of a study on a method for trapping gaseous impurities inthe exhaust gas, the inventors have developed the present invention byobtaining a knowledge that the exhaust gas is efficiently cooled byintroducing thereinto an operation fluid, which is in a supersonic stateby adiabatic expansion through a Laval nozzle, and thus the gaseousimpurities are condensed and/or coagulated to thereby be collected.

The present invention provides, a trap apparatus, installed in a vacuumexhaust system having a vacuum pump for vacuum exhausting a processingapparatus for performing a process on an object, for removing a gaseousimpurity contained in an exhaust gas flowing through the vacuum exhaustsystem, the trap apparatus including: an impurity collecting vesselinstalled in an exhaust passageway of the vacuum exhaust system; and anozzle unit for injecting an operation fluid to mix therewith theexhaust gas, and lowering an exhaust gas temperature down to or below acritical temperature of the impurity in the impurity collecting vessel,wherein the operation fluid is in a supersonic state by adiabaticexpansion.

As described above, by injecting the operation fluid adiabaticallyexpanded by the nozzle unit to thereby be in the supersonic state, theexhaust gas is cooled to condense and/or coagulate the gaseous impurity,to thereby trap them. Therefore, cooling efficiency can be kept high allthe time, and thus collection efficiency can be kept high all the time.Further, when performing a maintenance and repair operation forremoving, e.g., viscous captured materials, which have been condensedand/or coagulated to thereby be attached to impurity collecting vessel,the maintenance and repair operation can be carried out rapidly andeasily since complicated structures such as the cooling fins and thelike used for the conventional trap apparatus are not necessary.

In this case, the trap apparatus further includes one or more nozzleunits provided in parallel with each other with respect to the impuritycollecting vessel.

Further, the nozzle unit contains a nozzle main body configured to havea flow path whose cross section becomes narrower along a flow directionof the operation fluid, and then, becomes wider after passing a larynxportion.

Still further, the nozzle main body has an operation fluid injectionopening having a substantially circular cross section; and a ring shapedexhaust gas inlet opening is formed to surround a periphery of theoperation fluid injection opening to thereby introduce the exhaust gastowards the impurity collecting vessel.

Still further, the nozzle main body has an operation fluid injectionopening having a substantially ring shaped cross section; and, in acentral portion thereof, there is formed a substantially circularexhaust gas inlet opening for introducing the exhaust gas towards theimpurity collecting vessel.

Still further, there is provided a front end reservoir chamber fortemporarily reserving the exhaust gas flowing towards the exhaust gasinlet opening.

Still further, at a tip end side of the nozzle unit, there are provideda mixing tube for mixing the operation fluid in the supersonic stateinjected from the operation fluid injection opening and the exhaust gasintroduced from the exhaust gas inlet opening; and a diffusion tubewhose flow path cross section becomes gradually broader to have apumping function, wherein the mixing tube and the diffusion tube areconnected in sequence.

Still further, the mixing tube and the diffusion tube are provided withan adhesion prevention heater unit for preventing the impurity frombeing attached thereto by being condensed and/or coagulated.

In this manner, it is possible to prevent the impurities as, e.g.,viscous semisolid materials, from being attached to the inner wallsurfaces, since the mixing tube and the diffusion tube are heated by theadhesion prevention heater unit.

Still further, there is installed a nuclei introduction unit forintroducing a substance to be used as nuclei when the gaseous impurityis condensed and/or coagulated.

In this manner, the gaseous impurities are prevented from being in thesupercooled state to thereby facilitate the condensation and/orcoagulation by introducing nuclei to be origins (seeds) of transition tothe condensation and/or coagulation into the exhaust gas, so thatcollection efficiency of the impurities can be further improved.

Still further, in the impurity collecting vessel, there is attachablyand detachably installed an impurity adhesion plate for adhering thereona condensed and/or coagulated impurities.

Still further, the nozzle unit is a Laval nozzle.

Still further, the operation fluid is formed of N₂, H₂, Ar or He gas.

Still further, the processing apparatus is a film forming apparatus forperforming a film formation on the object.

Still further, the present invention provides a processing system,including: a processing apparatus for performing a process on an object;a vacuum exhaust system having a vacuum pump for vacuum exhausting theprocessing apparatus; and the trap apparatus of any one of claims 1 to13 installed in the vacuum exhaust system.

Still further, the present invention defines, a trap method performed byusing the above-described trap apparatus, and provides an impurityremoval method for removing a gaseous impurity from an exhaust gasdischarged from a processing apparatus which performs a process on anobject, the method including the step of: condensing and/or coagulatingthe impurity by mixing an operation fluid and the exhaust gas injectingthe operation fluid into the exhaust gas, the operation fluid being in asupersonic state by adiabatic expansion; and lowering an exhaust gastemperature down to or below a critical point of the impurity.

In this case, the exhaust gas is injected to surround a periphery of theoperation fluid when the exhaust gas and the operation fluid are mixed.

Further, the operation fluid is injected to surround a periphery of theexhaust gas when the exhaust gas and the operation fluid are mixed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 offers a schematic diagram of an exemplary processing system inwhich a trap apparatus in accordance with the present invention isprovided.

FIG. 2 is a cross sectional view showing a first embodiment of a trapapparatus in accordance with the present invention.

FIG. 3 provides a cross sectional view showing a second embodiment of atrap apparatus in accordance with the present invention.

FIG. 4 sets forth to a magnified cross sectional view of a nozzle unitin FIG. 3.

FIG. 5 presents a cross sectional view of a portion taken along A-A′line in FIG. 4.

FIG. 6 depicts a cross sectional view showing a third embodiment of atrap apparatus in accordance with the present invention.

FIG. 7 describes a magnified cross sectional view of a nozzle unit inFIG. 6.

FIG. 8 is a cross sectional view of a portion taken along B-B′ line inFIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of a trap apparatus, a processing system and animpurity removal method in accordance with the present invention will bedescribed below with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a schematic diagram of an exemplary processing system in whicha trap apparatus in accordance with the present invention is provided;and FIG. 2 is a cross sectional view showing a first embodiment of atrap apparatus in accordance with the present invention.

In the present embodiment, as an example, there will now be explained acase where a Ti film is formed on a surface of a semiconductor wafer,i.e., a substrate to be processed, by a plasma CVD (chemical vapordeposition) using as a source gas a refractory metal halogen compound,i.e., TiCl₄ gas.

As shown in FIG. 1, a processing system 2 includes a processingapparatus (film forming apparatus) 4 for performing a film formation ofa Ti film on a semiconductor wafer W; a vacuum exhaust unit 6 forexhausting an inside of the processing apparatus 4 to vacuum; and a trapapparatus 8 of the present invention, which is installed in the vacuumexhaust system 6.

First, the processing apparatus 4 will now be discussed. The processingapparatus 4 has, e.g., a barrel shaped processing vessel 10 made ofaluminum, wherein the processing vessel 10 is grounded. In theprocessing vessel 10, a mounting table 14 is provided through aconductive support 12 from a bottom portion, which mounts thereon thesemiconductor wafer W as an object to be processed. The mounting table14 is made of a conductive material, e.g., Ni or the like, and serves asa lower electrode having therein a resistance heater 16 for heating thesemiconductor wafer W.

Further, in a ceiling portion of the processing vessel 10, there isprovided a shower head 18 for introducing required gases, such as asource gas and the like, into the processing vessel 10 through aninsulating member 20; and a gas supply line 24 having therein a supplyside opening/closing valve 22 is connected to the shower head 18 tosupply therethrough the required gases, such as TiCl₄ gas, H₂ gas, Argas and the like at respectively controlled flow rates. Alternatively,the gases may be supplied through independent supply lines,respectively.

Still further, the shower head 18 serves as an upper electrode, and ahigh frequency power supply 28 of, e.g., 450 kHz, is connected theretovia a matching circuit 26 to produce a plasma by a high frequencybetween the mounting table 14 and the shower head 18. Here, thefrequency of the high frequency power supply 28 is not limited to 450kHz, but other frequencies, e.g., 13.56 MHz and the like, may beemployed.

Still further, on a sidewall of the processing vessel 10, there isprovided a gate valve 30 for loading/unloading the wafer W; and in aperiphery portion of a bottom portion, there is provided a gas exhaustport 32.

Meanwhile, the vacuum exhaust system 6 contains a stainless steelexhaust passageway 34 having an inner diameter of, e.g., about 10 cm,which is connected to the gas exhaust port 32. In this exhaustpassageway 34, there are installed the trap apparatus 8 for removinggaseous impurities from the exhaust gas; a vacuum pump 36 for vacuumpumping an atmosphere of the processing vessel 10; and a waste gasscrubber 38 for completely removing the impurity gases remaining in theexhaust gas, in this order towards the downstream side thereof.

Further, in an uppermost stream side of the exhaust passageway 34, thereis installed a pressure control valve 40 for controlling an innerpressure of the processing vessel 10 by changing a flow path crosssection of the exhaust passageway 34. At immediate downstream of thepressure control valve 40 in the exhaust passageway 34, there isprovided an ammonia gas nozzle 42 for injecting into the exhaustpassageway 34 an ammonia (NH₃) gas at a controlled flow rate. Theammonia gas is injected into the exhaust gas flowing therethrough, andreacts with a hydrogen chloride or a chorine gas contained in theexhaust gas to form an ammonium chloride and the like.

Still further, in an immediate upstream side and an immediate downstreamside of the trap apparatus 8 in the exhaust passageway 34, there areinstalled opening/closing valves 44 for separating the trap apparatus 8from the exhaust passageway 34 when it is attached/detached. Moreover,the gas supply line 24 and the exhaust passageway 34 between theprocessing vessel 10 and the trap apparatus 8 are wrapped with tapeheaters 46A and 46B, respectively, as indicated by dotted lines in thedrawing. Thus, the impurity gases flowing through the respectivepassageways 24 and 34 are heated to temperatures higher than criticaltemperatures thereof (condensation temperatures or coagulationtemperatures) to prevent the impurity gases from being liquefied orsolidified inside the passageways 24 and 34.

Still further, as shown in FIG. 2, the trap apparatus 8 in accordancewith the present invention includes a box shaped impurity collectingvessel 50 made of aluminum. In a ceiling portion of the impuritycollecting vessel 50, there is formed a gas inlet 52, connected to theexhaust passageway 34 extending from an upstream side, for introducingthe exhaust gas therethrough. Moreover, at one sidewall of the impuritycollecting vessel 50, there is formed a gas outlet 54, connected to theexhaust passageway 34 extending towards the downstream side thereof, fordischarging gases towards the downstream side. Therefore, the exhaustgas from which the gaseous impurities have been removed is dischargedtowards the downstream. Here, the installation positions of the gasinlet 52 and the gas outlet 54 are not specifically limited thereto.

Still further, another sidewall of the impurity collecting vessel 50serves as, e.g., an opening/closing door 56 configured to be opened andclosed, which is opened or closed when the maintenance, repair and thelike need to be performed. The opening/closing door 56 is airtightlysealed through a sealing member 58 such as an O-ring or the like.Moreover, on a substantially entire surface of the bottom portion insidethe impurity collecting vessel 50, there is equipped an impurityadhesion plate 60 configured to be attached thereto or detachedtherefrom, such that liquid phase impurities, which are condensed and/orcoagulated to have, e.g., high viscosity, or condensed and/or coagulatedimpurities M (see FIG. 2), are to be deposited on a top surface thereof.

Still further, a nozzle unit 64, being a characteristic feature of thepresent invention, is provided in the ceiling portion of the impuritycollecting vessel 50 facing the impurity adhesion plate 60. An operationgas source 68 storing, e.g., N₂ gas, as an operation fluid, is connectedto the nozzle unit 64 through an operation gas line 66, such that the N₂gas having a specified pressure is supplied to the nozzle unit 64.Moreover, in the operation gas line 66, there is installed anopening/closing valve 70 controlling the N₂ gas supply. In an upstreamside right above the nozzle unit 64 in the operation gas line 66, thereis installed a nuclei introduction unit 72 for introducing a substanceto be nuclei in the operation fluid when the gaseous impurities arecondensed and/or coagulated.

As for the nuclei introduction unit 72 for introducing nuclei to beorigins (seeds) of transition to the condensation and/or coagulation,there is provided a gas nozzle 72A, equipped in the operation gas line66, for introducing as nuclei a vapor at a controlled flow rate. By sucha configuration, the operation fluid (N₂ gas) is injected in asupersonic state from the nozzle unit 64. As a result, the operationfluid, which is in the supersonic state by the adiabatic expansion, isblown into the impurity collecting vessel 50 to cool the exhaust gas bybeing mixed therewith, and thus the gaseous impurities are cooled belowthe critical temperatures to be condensed and/or coagulated.

In this case, the nozzle main body 74 forming the nozzle unit 64 asshown in FIG. 2 is configured such that a flow path cross area becomesgradually narrower along a flow direction of the operation fluid at acenter side thereof; and becomes gradually broader after passing alarynx portion 74A wherein the flow path cross section is the narrowest.Thus, a lowest end portion serves as an operation fluid injectionopening 74C having a substantially circular cross section. As for thenozzle unit 64, a Laval nozzle may be used, for example.

In the following, an impurity removal method to be performed by usingthe processing system as configured above will be explained.

First, when performing a film formation of a Ti film, a semiconductorwafer W is mounted on the mounting table 14 inside the processing vessel10 of the processing apparatus 4 and heated to a predeterminedtemperature. At the same time, a high frequency power is applied betweenthe mounting table 14 as a lower electrode and the shower head 18 as anupper electrode; specified gases, such as TiCl₄ gas, H₂ gas, Ar gas andthe like, are supplied from the shower head 14 while flow rates thereofare controlled; and thus a plasma is generated in a processing space toperform a film formation of a Ti film. Simultaneously, the vacuumexhaust system 6 is operated to vacuum exhaust the atmosphere of theprocessing vessel 10 to thereby maintain the inside thereof at apredetermined pressure.

At this time, given that a size of a wafer is 8 inch, process conditionsmay be set such that a process pressure is 665 Pa (≈5 Torr); a processtemperature is about 650° C.; a flow rate of TiCl₄ gas is about 5 sccm;a flow rate of H₂ gas is about 2000 sccm; and a flow rate of Ar gas isabout 500 sccm.

By the film forming reaction of the Ti film, TiCl₄ gas is consumed about10%. However, the remaining 90% thereof is discharged with the exhaustgas as an unreacted gas or reaction by-products such as TiCl₂, TiCl₃,HCl and the like, from the gas exhaust port 32 to and through theexhaust passageway 34 of the vacuum exhaust system 6, and flows throughthe trap apparatus 8, the vacuum pump 36, and the waste gas scrubber 38in that order. Here, specifically, TiCl₄ gas in the unreacted gas or thereaction by-products is hardly trapped since it has a relatively highvapor pressure. However, since NH₃ gas is introduced as a reactive gasfrom the ammonia gas nozzle 42 into the exhaust passageway 34, it reactswith TiCl₄ gas mainly to thereby form a compound formed of a TiCl₄₀.2NH₃complex. A vapor pressure of this complex is much lower than that ofTiCl₄ gas. For example, TiCl₄ gas has a vapor pressure of 1300 Pa at21.3° C., and the complex has a vapor pressure of 1×10⁻⁴ Pa at 21.3° C.In addition, HCl gas becomes NH₄Cl gas by reacting with NH₃ gas, andNH₄Cl also has a low vapor pressure.

As described above, the unreactive residual gas mainly reacts with NH₃gas to thereby be converted into a low vapor pressure compound and HClas the reaction by-product reacts with NH₃ gas to thereby be convertedinto a low vapor pressure compound, so that they are relatively easilytrapped in the trap apparatus 8. The gaseous impurities including thecomplex, NH₄Cl and the like are introduced into the impurity collectingvessel 50 through the gas inlet 52 of the trap apparatus 8, by beingcontained in the exhaust gas.

Here, N₂ gas as an operation fluid, which is in the supersonic state bythe adiabatic expansion, is injected into the impurity collecting vessel50 through the nozzle unit 64 provided at the ceiling portion thereof.Such N₂ gas is mixed with the exhaust gas while the temperature thereofis lowered by itself by the adiabatic expansion (referred to as aself-cooling). In this way, the exhaust gas is cooled, so that thegaseous impurities are cooled below the critical temperatures to therebybe condensed and/or coagulated, and deposited. The impurities M areattached and deposited on the impurity adhesion plate 60 provided on thebottom portion of the impurity collecting vessel 50 to thereby betrapped thereon. The exhaust gas from which the gaseous impurities havebeen removed as described above is discharged through the gas outlet 54and flows towards the vacuum pump 36 of the downstream side.

As mentioned above, there is utilized a nozzle, e.g., a Laval nozzle,capable of realizing a supersonic state by converting the pressuredifference into a kinetic energy of N₂ gas, which is an operation fluid;and thus the gaseous impurities are cooled to be condensed and/orcoagulated by a self-cooling when the N₂ gas is adiabatically expandedto be a supersonic state. Therefore, the gaseous impurities can beefficiently removed from the exhaust gas.

Further, since the cooling fins and the like, which are used in theconventional trap apparatus, are not employed, cooling efficiency can bekept high all the time. Still further, even though the capturedimpurities are increased, it does not adversely affect exhaustconductance. Still further, since the cooling fins and the like are notused, as mentioned above, the entire configuration of the trap apparatus8 can be simplified. At this time, the flow rate of the operation fluidis configured not to adversely affect the pressure control inside theprocessing vessel 10 of the upstream side.

Still further, in the N₂ gas of the operation fluid, there is containeda vapor introduced from the nuclei introduction unit 72. The vapor iscooled in the impurity collecting vessel 50 to become fine ice particlesserving as nuclei so that the gaseous impurities are condensed and/orcoagulated by using the ice particles as nuclei without beingsupercooled. As a result, collection efficiency of the impurities can befurther increased. Moreover, the nuclei introduction unit 72 may beprovided in the impurity collecting vessel 50 to directly introduce thevapor into the impurity collecting vessel 50. This is the same as inother embodiments that will be discussed later.

Still further, the maintenance and repair of the trap apparatus 8 isperformed such that the opening/closing door 56 is separated to unloadthe impurity adhesion plate 60 configured to be attached and detachedfrom the impurity collecting vessel 50, and the impurities M adhered onthe impurity adhesion plate 60 are cleaned and removed. Thus,maintenance workability can be considerably enhanced.

For easy understanding of the present invention, in the firstembodiment, an example of employing one nozzle unit 64 has beendescribed. However, multiple nozzle units 64 may be provided in parallelwith each other to inject into the impurity collecting vessel 50 theoperation fluid in which the vapor is contained.

Second Embodiment

Next, a second embodiment of the present invention will be discussed. Inthe second embodiment, the configuration of the nozzle unit 64 in thepreviously described first embodiment is slightly modified, and aplurality of nozzle units is provided in parallel with each other.

FIG. 3 is a cross sectional view showing the second embodiment of a trapapparatus in accordance with the present invention; FIG. 4 is amagnified cross sectional view of one nozzle unit in FIG. 3; and FIG. 5is a cross sectional view of a portion taken along A-A′ line in FIG. 4.Further, parts having substantially the same configurations as thosedescribed in FIGS. 1 and 2 are designated by the same referencenumerals, and their redundant explanations will be omitted unlessnecessary.

As shown in the drawings, at a front end side of the impurity collectingvessel 50, there is provided, e.g., a stainless steel front endreservoir chamber 80 for temporarily storing or reserving the exhaustgas flowing from the processing vessel 10 side. A gas inlet 82 isprovided at one sidewall portion of the front end reservoir chamber 80;and the exhaust gas flows thereinto through the gas inlet 82 connectedto the upstream side of exhaust passageway 34.

Further, between a sidewall in the longitudinal direction of the frontend reservoir chamber 80 and the ceiling portion 62 of the impuritycollecting vessel 50, there are provided multiple, e.g., nine in thedrawing, communication passageways 84 in parallel with each other forallowing for the front end reservoir chamber 80 to communicate with theimpurity collecting vessel 50. Through the communication passageways 84,the exhaust gas in the front end reservoir chamber 80 flows into theimpurity collecting vessel 50. As shown in FIG. 4, each of thecommunication passageways 84 is formed of a cone shaped introductiontube 86 whose inner diameter becomes gradually smaller along the flowdirection of the exhaust gas; a cylindrical shape mixing tube 88connected to the introduction tube 86; and a diffusion tube 90,connected to the mixing tube 88, whose inner diameter becomes graduallylarger along the flow direction of the exhaust gas.

Meanwhile, in the front end reservoir chamber 80, there is providedoperation gas header 92 of a specified size, connected to the operationgas line 66, into which the operation gas containing a vapor whichbecomes an origin of transition to the condensation and/or coagulationis introduced. Further, the respective nozzle units 64 having the sameconfiguration as in FIG. 2 are installed extending from the operationgas header 92 towards the respective communication passageways 84. Asshown in FIG. 4, a tip end portion of the nozzle main body 74 in eachnozzle unit 64 is placed around joint portion between the introductiontube 86 and the mixing tube 88 without making any contact with them.

Accordingly, as shown in FIG. 5, in this part, an operation fluidinjection opening 74C having a substantially circular cross section isformed in the central portion; and an exhaust gas inlet opening 94having a substantially ring shaped cross section is formed to surroundthe periphery of the operation fluid injection opening 74C. Thus, theexhaust gas is introduced towards the impurity collecting vessel 50through the exhaust gas inlet opening 94. Here, as mentioned above, thenozzle main body 74 is configured such that the flow path cross areabecomes gradually narrower along the flow direction of the operationfluid in the center side thereof and becomes gradually broader afterpassing the larynx portion 74A wherein the flow path cross section isthe narrowest. Thus, the lowest end portion thereof serves as theoperation fluid injection opening 74C having a substantially circularcross section. As for the nozzle unit 64, the above-described Lavalnozzle may be used, for example.

As described above, if the operation fluid of the supersonic state isinjected from the nozzle units 64, the nozzle units 64 have pumpingfunctions such as an ejector pump and the exhaust gas from the exhaustgas inlet opening 94 is washed away by an ejection stream of theoperation fluid to thereby run towards exhaust side.

Further, on outer peripheral walls of the mixing tube 88 and thediffusion tube 90, there are provided adhesion prevention heater units96, e.g., tape heater. By heating the adhesion prevention heater units96 to temperatures higher than the critical temperatures of the gaseousimpurities, the impurities are prevented from being condensed and/orcoagulated in the inner wall surfaces thereof, and thus being attachedthereto.

In case of the second embodiment, basically the same operation andeffect as in the aforementioned first embodiment could be obtained. Forexample, the exhaust gas flowing from the processing vessel 10 side isdiffused entirely in the front end reservoir chamber 80, and isintroduced into the impurity collecting vessel 50 in parallel throughthe respective communication passageways 84. At the same time, theoperation fluid, e.g., N₂ gas, is injected in the supersonic state bythe adiabatic expansion, through the operation fluid injection opening74C of each nozzle unit 64 via the operation gas header 92. Thesupersonic state of N₂ gas is diffused in the diffusion tube 90 whilebeing mixed in the mixing tube 88 with the exhaust gas introduced fromthe ring shaped exhaust gas inlet opening 94, and reaches the impuritycollecting vessel 50, wherein the gaseous impurities are cooled to becondensed and/or coagulated, so that the impurities M are adhered on theimpurity adhesion plate 60. Accordingly, same as in the firstembodiment, the impurities can be efficiently removed from the exhaustgas. Specifically, since the multiple nozzle units 64 are provided inparallel with each other, removal efficiency of the impurities can beincreased.

Further, by introducing the nuclei, e.g., vapor, into the operationfluid, the gaseous impurities are not supercooled like in the firstembodiment, so that removal efficiency of the impurities can be furtherincreased. While the conventional trap apparatus lowers exhaustconductance, the nozzle units 64 of the second embodiment exhibitpumping functions such that the exhaust gas from the ring shaped exhaustgas inlet port 94 provided around the operation fluid injection opening74C is sucked to thereby be washed away towards exhaust side. Therefore,exhaust conductance can be increased, and the exhaust system is notadversely affected. Moreover, the adhesion prevention heater units 96are provided at the mixing tube 88 and the diffusion tube 90, so thatthe impurities can be prevented from being attached to the inner wallsurface sides.

As a result of a study for parameters such as temperature, pressure, gasvelocity and the like, in each part of the configuration shown in FIG.4, the following results could be obtained.

Operation fluid pressure at nozzle inlet P1: 1.33×10⁴ Pa (≈0.1 atm)

Gas temperature T1 of operation fluid inside the operation gas source68: 293 K (20° C.)

Gas velocity U1 of operation fluid at nozzle inlet: 0.0 m/s (it can betreated as zero compared with the supersonic speed)

Specific heat ratio k of gas: 1.4

Exhaust gas pressure Pe2 at the exhaust gas inlet opening 94: 133 Pa

Exhaust gas temperature Te2 at the exhaust gas inlet opening 94: 423 K(150° C.)

Exhaust gas velocity Ue2 at the exhaust gas inlet opening 94: 328.2 m/s

Area Se of the exhaust gas inlet opening 94: 808.5 mm²

Area Sn of the operation fluid injection opening 74C: 1155.0 mm²

Diameter D1 of the mixing tube 88: 50.0 mm

Outlet diameter D2 of the diffusion tube 90: 53.9 mm

When setting the parameters as described above, the following resultswere obtained.

Pressure Pn2 at nozzle outlet: 133 Pa (≈0.001 atm)

Operation fluid temperature Tn2 at nozzle outlet: 78.6 K (−194.4° C.)

Operation fluid velocity Un2 at nozzle outlet: 656.4 m/s (supersonicstate)

Pressure P4 at outlet of the mixing tube 88: 133 Pa

Temperature T4 of gaseous mixture at outlet of the mixing tube 88: 150.8K (−122.2° C.)

Velocity U4 of gaseous mixture at outlet of the mixing tube 88: 413.3m/s

Pressure P5 at outlet of the diffusion tube 90: 189.9 Pa

Temperature T5 of gaseous mixture at outlet of the diffusion tube 90:167.0 K (−106.0° C.)

Velocity U5 of gaseous mixture at outlet of the diffusion tube 90: 372m/s

As described above, it could be secured that the temperature of thegaseous mixture is kept very low until the operation fluid reaches theimpurity collection vessel 50 via the mixing tube 88 and the diffusiontube 90 after being injected from the outlet of the nozzle in thesupersonic state.

Third Embodiment

Next, a third embodiment of the present invention will be discussed. Thethird embodiment is configured such that central sides and outerperiphery sides of the nozzle units 64 of the previously describedsecond embodiment are reversed. In such a configuration, the operationfluid is injected through the outer periphery sides and the exhaust gasflows through the central sides.

FIG. 6 is a cross sectional view showing the third embodiment of a trapapparatus in accordance with the present invention; FIG. 7 is amagnified cross sectional view of one nozzle unit in FIG. 6; and FIG. 8is a cross sectional view of a portion taken along B-B′ line in FIG. 7.Further, parts having substantially the same configurations as thosedescribed in FIGS. 3 to 5 are designated by the same reference numerals,and their redundant explanations will be omitted unless necessary.

As shown in the drawings, same as in the second embodiment, at a frontend side of the impurity collecting vessel 50, there is provided astainless steel front end reservoir chamber 80 for temporarily storingor reserving the exhaust gas flowing from the processing vessel 10 side.A gas inlet 82 is provided at one sidewall portion of the front endreservoir chamber 80; and the exhaust gas flows thereinto through thegas inlet 82 connected to the upstream side of exhaust passageway 34.

Further, there are installed multiple, e.g., six in the drawing, nozzlemain bodies 100 extending from the sidewall in the longitudinaldirection of the front end reservoir chamber 80 towards the impuritycollecting vessel 50. Moreover, between the front end reservoir chamber80 and the impurity collecting vessel 50, there is installed anoperation gas header 92 of a specified size connected to the operationgas line 66.

Still further, between the sidewall in the longitudinal direction of theoperation gas header 92 and the ceiling portion 62 of the impuritycollecting vessel 50, there are provided multiple, e.g., six in thedrawing, communication passageways 102 to allow for the operation gasheader 92 to communicate with the impurity collecting vessel 50. Throughthe communication passageways 102, the operation fluid in the operationgas header 92 flows into the impurity collecting vessel 50. As shown inFIG. 7, each of the communication passageways 102 is formed of a coneshaped introduction tube 104 whose inner diameter becomes graduallysmaller along the flow direction of the operation fluid; a cylindricalshape mixing tube 106 connected to the introduction tube 104; and adiffusion tube 108, connected to the mixing tube 88, whose innerdiameter becomes gradually larger along the flow direction of theexhaust gas (operation fluid).

Here, a nozzle outer container 110 is formed of the introduction tube104 and the mixing tube 106; and a nozzle unit 120 is formed of thenozzle outer container 110 and the nozzle main body 100. Specifically,the nozzle main body 100 airtightly penetrates one sidewall of theoperation gas header 92 to be inserted in the header; and a tip endportion of the nozzle main body 100 reaches into the mixing tube 106without making any contact therebetween. Further, at an outer peripheryof the tip end portion of the nozzle main body 100, there is formed aring shaped passage narrowing portion 112 having a protruded shape ofcross section where a flow path cross area becomes gradually narroweralong the flow direction of the operation fluid and becomes graduallybroader after passing a larynx portion 100A wherein the flow path crosssection is the narrowest. Thus, the pressure difference between Xportion and Y portion (see FIG. 7), when the operation fluid passes thelarynx portion 100A and the narrowing portion 112, is efficientlyconverted into a velocity, so that the supersonic state can be realizedat a lower temperature.

Accordingly, as shown in FIG. 8, an exhaust gas inlet opening 114 havinga substantially circular cross section is formed in the central portion;and an operation fluid injection opening 100C having a substantiallyring shaped cross section is formed to surround the periphery of theexhaust gas inlet opening 114. Thus, the exhaust gas is introducedtowards the impurity collecting vessel 50 through the exhaust gas inletopening 114. Further, the operation fluid is injected from the operationfluid injection opening 100C. Still further, the passage narrowingportion 112 having a protruded shape of cross section may be provided inan inner side of the mixing tube 106 instead of being provided in thenozzle main body 100 side, or it may be provided in both sides. Inaddition, it may adopt various shapes, as long as so-called Laval nozzlecapable of injecting the operation fluid in the supersonic state can beformed.

The third embodiment can exhibit the same operation and effect as in theprevious first and second embodiments. Namely, the exhaust gas isdischarged through the exhaust gas inlet opening 114 via the center ofthe nozzle main body 100; and the N₂ gas of the operation fluid isinjected from the ring shaped operation fluid injection opening 100Cthrough the introduction tube 104 and the larynx portion 100A from theoperation gas header 92. At this time, the N₂ gas is adiabaticallyexpanded to thereby be cooled by the self-cooling, so that it isinjected at a lower temperature in the supersonic state. Thus, asmentioned above, the gaseous impurities are made to be condensed and/orcoagulated by sucking the exhaust gas. In this case, like in the secondembodiment, the nozzle unit 120 exhibits pumping function to therebyprevent exhaust conductance from being adversely affected.

Further, in the third embodiment, it is possible to prevent the exhaustgas from being directly contacted with the inner wall surface of themixing tube 106 and the diffusion tube 108, since the N₂ gas of theoperation fluid flows to surround the periphery of the exhaust gas.Therefore, it is possible to prevent the condensed and/or coagulatedimpurities from being attached to the inner wall surface of the mixingtube 106 and the diffusion tube 108. Moreover, in the third embodiment,like in the second embodiment, there may be provided the adhesionprevention heater units 96 for completely preventing the impurities frombeing attached thereto.

Still further, in the respective embodiments, the vapor has beenintroduced and frozen to form nuclei, which become origins of transitionto the condensation and/or coagulation, but it is not limited thereto. Apowder such as ceramic, quartz or the like may be employed. In addition,the operation fluid is not limited to the N₂ gas, and an inactive gassuch as Ar gas, He gas or the like, H₂ gas and the like, may be used.

Still further, a film species to be formed is not limited to the Tifilm; and the present invention may be adopted to all film formingapparatus or processing apparatus wherein reaction by-products orunreacted materials need to be removed from the exhaust gas.

Still further, in the respective embodiments, examples of using thesemiconductor wafer as the substrate to be processed have beendescribed, but it is not limited thereto. A glass substrate, an LCDsubstrate or the like may be used.

As mentioned above, in accordance with a trap apparatus, a processingsystem and an impurity removal method of the present invention, theoperation fluid adiabatically expanded by the nozzle unit to thereby bein the supersonic state is injected into the exhaust gas, so that theexhaust gas is cooled to condense and/or coagulate the gaseousimpurities, to thereby trap them. Therefore, cooling efficiency can bekept high all the time, and thus collection efficiency can be kept highall the time. Further, when performing a maintenance and repairoperation for removing, e.g., viscous captured materials, which havebeen condensed and/or coagulated to thereby be attached to impuritycollecting vessel, the maintenance and repair operation can be carriedout rapidly and easily since complicated structures such as the coolingfins and the like used for the conventional trap apparatus are notnecessary. Still further, since the mixing tube and the diffusion tubeare heated by the adhesion prevention heater unit, it is possible toprevent the impurities as, e.g., viscous semisolid materials, from beingattached to the inner wall surfaces. Still further, the gaseousimpurities are prevented from being in the supercooled state to therebyfacilitate the condensation and/or coagulation by introducing nucleiinto the exhaust gas, so that collection efficiency of the impuritiescan be further improved.

1. A trap apparatus, installed in a vacuum exhaust system having avacuum pump for vacuum exhausting a processing apparatus for performinga process on an object, for removing a gaseous impurity contained in anexhaust gas flowing through the vacuum exhaust system, the trapapparatus comprising: an impurity collecting vessel installed in anexhaust passageway of the vacuum exhaust system; and a nozzle unit forinjecting an operation fluid to mix therewith the exhaust gas, andlowering an exhaust gas temperature down to or below a criticaltemperature of the impurity in the impurity collecting vessel, whereinthe operation fluid is in a supersonic state by adiabatic expansion. 2.The trap apparatus of claim 1, further comprising one or more nozzleunits provided in parallel with each other with respect to the impuritycollecting vessel.
 3. The trap apparatus of claim 1, wherein the nozzleunit includes a nozzle main body configured to have a flow path whosecross section becomes narrower along a flow direction of the operationfluid, and then, becomes wider after passing a larynx portion.
 4. Thetrap apparatus of claim 3, wherein the nozzle main body has an operationfluid injection opening having a substantially circular cross section;and a ring shaped exhaust gas inlet opening is formed to surround aperiphery of the operation fluid injection opening to thereby introducethe exhaust gas towards the impurity collecting vessel.
 5. The trapapparatus of claim 3, wherein the nozzle main body has an operationfluid injection opening having a substantially ring shaped crosssection; and, in a central portion thereof, there is formed asubstantially circular exhaust gas inlet opening for introducing theexhaust gas towards the impurity collecting vessel.
 6. The trapapparatus of claim 4, wherein there is provided a front end reservoirchamber for temporarily reserving the exhaust gas flowing towards theexhaust gas inlet opening.
 7. The trap apparatus of claim 4, wherein, ata tip end side of the nozzle unit, there are provided a mixing tube formixing the operation fluid in the supersonic state injected from theoperation fluid injection opening and the exhaust gas introduced fromthe exhaust gas inlet opening; and a diffusion tube whose flow pathcross section becomes gradually broader to have a pumping function,wherein the mixing tube and the diffusion tube are connected insequence.
 8. The trap apparatus of claim 7, wherein the mixing tube andthe diffusion tube are provided with an adhesion prevention heater unitfor preventing the impurity from being attached thereto by beingcondensed and/or coagulated.
 9. The trap apparatus of claim 1, whereinthere is installed a nuclei introduction unit for introducing asubstance to be used as nuclei when the gaseous impurity is condensedand/or coagulated.
 10. The trap apparatus of claim 1, wherein, in theimpurity collecting vessel, there is attachably and detachably installedan impurity adhesion plate for adhering thereon a condensed and/orcoagulated impurities.
 11. The trap apparatus of claim 1, wherein thenozzle unit is a Laval nozzle.
 12. The trap apparatus of claim 1,wherein the operation fluid is formed of N₂, H₂, Ar or He gas.
 13. Thetrap apparatus of claim 1, wherein the processing apparatus is a filmforming apparatus for performing a film formation on the object.
 14. Aprocessing system, comprising: a processing apparatus for performing aprocess on an object; a vacuum exhaust system having a vacuum pump forvacuum exhausting the processing apparatus; and the trap apparatus ofclaim 1 installed in the vacuum exhaust system.
 15. An impurity removalmethod for removing a gaseous impurity from an exhaust gas dischargedfrom a processing apparatus which performs a process on an object, themethod comprising the step of: condensing and/or coagulating theimpurity by mixing an operation fluid and the exhaust gas injecting theoperation fluid into the exhaust gas, the operation fluid being in asupersonic state by adiabatic expansion; and lowering an exhaust gastemperature down to or below a critical point of the impurity.
 16. Theimpurity removal method of claim 15, wherein the exhaust gas is injectedto surround a periphery of the operation fluid when the exhaust gas andthe operation fluid are mixed.
 17. The impurity removal method of claim15, wherein the operation fluid is injected to surround a periphery ofthe exhaust gas when the exhaust gas and the operation fluid are mixed.